IL-6 is a pleiotropic proinflammatory cytokine produced and secreted by a wide variety of cell types, most notably antigen presenting cells, T and B cells. IL-6 is involved in such diverse activities as B cell growth and differentiation, T cell activation, hematopoiesis, osteoclast activation, keratinocyte growth, neuronal growth and hepatocyte activation.
IL-6 plays an important role in B cell abnormalities as demonstrated in systemic lupus erythematosus, multiple myeloma and lymphoproliferative disorders. Similarly, IL-6 is also implicated in the pathogenesis of autoimmune and inflammatory diseases, such as rheumatoid arthritis and osteoarthritis. Evidence also suggests an association between IL-6 and chronic obstructive pulmonary disease and insulin resistance in type 2 diabetes. IL-6 has both pro-inflammatory and anti-inflammatory effects in the immune system, indicating that this cytokine likely plays a central role in regulating the physiological response to disease. Therefore, targeting IL-6 can potentially provide therapeutic benefit in a variety of disease areas.
An increase in the production of IL-6 has been observed in a number of diseases including: Alzheimer's disease, autoimmune diseases, such as rheumatoid arthritis, inflammation, myocardial infarction, Paget's disease, osteoporosis, solid tumors (renal cell carcinoma), prostatic and bladder cancers, neurological cancers, and B-cell malignancies (e.g., Casteleman's disease, certain lymphomas, chronic lymphocytic leukemia, and multiple myeloma). Research has indicated that IL-6 is linked to the pathogenesis of many of these diseases, particularly, cancer and, therefore, blocking IL-6 should translate into clinical benefits.
IL-6 induces signaling through a cell surface heterodimeric receptor complex composed of a ligand binding subunit (gp80) and a signal transducing subunit (gp130). IL-6 is able to bind gp80, but does not bind to gp130 unless in the presence of gp80.
The cDNA for human gp80 has been isolated (Yamasaki et al., 1988, Science 241), and was found to be 1407 bp in length. Human gp80 cDNA encodes a 468 amino acid protein, having a 19 amino acid signal peptide and a domain of approximately 90 amino acids that is similar to a domain in the immunoglobulin superfamily. The cytoplasmic domain of approximately 82 amino acids lacks a tyrosine/kinase domain, unlike other growth factor receptors. The mature human protein has a calculated molecular weight of 51.6 kDa. A soluble form of gp80 has been reported (Novick et al., 1989, J. Exp. Med. 170) which arises from proteolytic cleavage of membrane-bound gp80. This soluble receptor has been shown to bind to IL-6 in solution (Yasukawa et al., 1990, J. Biochem. 108)
Extensive safety testing is required for an IL-6 or gp80 (IL-6R) human therapeutic to be brought to the marketplace. Such safety testing involves both in vivo safety testing in animal models as well as the in vitro testing of these therapeutics. For example, antibody based IL-6 and gp80 therapeutics may require the generation of surrogate antibodies against an IL-6 or gp80 peptide chain expressed by a particular model animal as well as significant in vitro characterization of such surrogate antibodies. Such surrogate generation and in vitro characterization may require the use of IL-6 and gp80 polynucleotides and peptide chains from a suitable model animal. Importantly, the identification of suitable animal models for such safety testing requires the identification of animal species capable of expressing a gp80 with high identity and homology to human gp80 (SEQ ID NO:11).
Thus, a need exists for the identification of polynucleotides encoding gp80s and gp80 peptide chains capable of being expressed in an animal model suitable for the safety testing of IL-6 and gp80 therapeutics. A need also exists for related methods such as methods of expressing peptide chains and testing the safety of an IL-6 or gp80 therapeutic in an animal model identified as suitable for safety assessment of IL-6 or gp80 therapeutics.